Analytical reagent and method



y 5, 1953 B. GEHAUF ET'AL ANALYTICAL REAGENT AND METHOD Filed March 9 1949 0 E 0205.235 2. E023 w 000 00\. 000 00m 000 0 52005 00 60 00;

000 0n z. 000 2 00 040 0 000l||0fi K o o v z m0z m0 $303030 0.6 60 200; @300 0m a cm on H Q Q m B\ 3 l 00 09m 000 00 000 00m 000 0 000 2.0.0. 000 000 0 M 293140 0mm m zwmmomfim u 350; 1 @0400 2003 x300 J w 00 00 o 3 BERNARD GEHAUF 3 and JEROME GOLDENSON Patented May 5, 1 953 ANALYTICAL REAGENT'AND METHOD Bernard Gehauf and Jerome Goldenson Baltimore, Md.

Application March 9, 1949-, serial No. 80,553 6 Claims. (01. as -230') (Granted under Title 35, U.- S. Code (1952), see. 266) This invention relates to chemical analysis, particularly to a novel method involving thereaction of thio-Michlers ketone, (p D'-bis(dimeth ylamino) thiobenzophenone), hereinafter referred to as TMK, with metallic ions, and to certain novel compounds resulting therefrom. The subject matter contained herein also disclosed in part in applicants copending application, Serial No. 80,554.

One object of the present invention is to provide a novel method for detecting and determining trace amounts of certain metals.

- A further object is to produce from the aforementioned method a novel means for determin-- ing trace amounts of cy'anides and of carbon monoxide. v

Other objects will more plainly appear from the detailed specification and drawing presented herewith in exemplification but not in limitation or the present invention.

A clarification of one manifestation of the pres ent invention is shown in the accompanying drawing, which illustrates diagrammatically in the figure absorption sp'ectro charts illustrating certain of the metallic compounds of the pros ent invention.

During the investigation of color changes produced. in the oxidation of a number of organic compounds it was found that TMK formed a compound of intense blue-green color when added to a mercuric chloride solution. The colored substance, surprisingly, was found to be a definite compound of TMK and mercuric chloride instead of an oxidation productwhich it was first presumed to be. When the reaction was tried using salts of other metals it was found that similar compounds of. different colors were obtained with cuprou's salts of copper, and with salts of gold; platinum, silver, pal-adium, but not with salts of other metals. This selectivity of TMK for a oertain group of metals to form intensely colored compounds indicated an entirely unexpected value as a reagent for inorganic analysis. This important, novel use of these colored metallic derivatives is unusually remarkable in view of the intensive search in the past two decades for suitable reagents for metallic ions;

TMK is a purplish-red crystalline substance, practically insoluble in water, but readily soluble in certain organic solvents to which it imparts a yellow color. It can be prepared: from dimethylaniline by treatment with thiophosgene; or by melting tetramethyldiaminodiphenylmethane and sulfur together; but preferably it is prepared from auramine by treatment with hydrogen sulride.

It has been assumedthat the structure of the metall c derivatives of TMK would be typified by the following addition product with silver nitrate:

assumption is based on the high intensity of color of these compounds in aqueous solution suggesting a structure closely resembling that assigned to diphenylmethane dyes. This is imther'borneoiit by the ap earance of the crystali'z'ed metallic compounds, which are all deeply coloredand exhibit the metallic reflex characteristic of intensely colored dye Substances. Although the omain structure alone would account for the high color intensity of these substances, the metal content is an important factor, since the colors of the different compounds vary considerably according to the metal present in the compound. The mercury compound, for instance, as indicated in the figure, is blue-green a strong red dichroism, the gold compound is par 1e, and the silver com ound is magenta.

Che many. the metal derivatives of TMK act as salts of the metal. Thus the mercury compound reacts quantitatively with cyanides', formmg mercuric cyanide and free TMK. This reactivity permits the use of the colored complexes as internal indicators for volumetric analysis of metals or a number of novel analytical methads in which the metals ai used as reagents.

All the reagents used to demonstrate the present invention are standard C. P. chemicals, with the exception of TMK which was prepared at the Experimental Station of the E. I. du Pont de Nemours Company, Wilmington, Delaware. Analysis of this material showed the following composition:

. Found, Per- Calculated.

cent Percent Nitrogen 9. s 9 35 Smiur 10.9 11127 Carbon 71-9 71.79 Hydrogen 7. 1 7. 09

. buffered with 1- mi. of a 10% sodium acetate solution and then treated with 1 drop of 0.1% acetone solution of TMK. The sodium acetate is added to prevent any traces of free C12 in the water from reacting with the indicator. The test may be observed in a %,-in. test tube viewed from above and compared with a prepared blank. In making up the copper solutions cupric acetate is used; after buffering with sodium acetate a small quantity of hydroxylamine is added to obtain the cuprous state required for reaction with TMK. It is found that paladium solutions react slowly unless additional acetone (1 m1.) be added prior to the test.

The sensitivities found were:

One part in Hg 5,000,000 Ag 5,000,000 Cu(ous) 1,000,000 Au 1,000,000. Pd 10,000,000 i The mercury compound is prepared by treating a saturated solution of TMK in acetone with an excess of aqueous mercuric chloride solution. After standing for several hours the mercury compound is crystallized as deep colored, needle-like crystals with an intense green metallic reflex. Although the other metallic derivatives of the present invention are not obtained in crystallized form in the same manner, they are pree pared by extracting the aqueous solutions with chloroform and evaporating the extract to dryness. Dark colored, microcrystalline deposits, resembling the mercury compound in appearance, are formed. The gold compound is also obtained as well defined crystals by mixing ether solutions of chloroauric acidand TMK. All of the solid compounds are found to be soluble to a limited extent inwater and very freely in chloroform, a1- cohol, and acetone. Solubility in ether or aromatic liquids was negligible.

Aqueous solutions of the various metallic compounds of the present invention are prepared by reacting buffered solutions of the salts with an acetone solution of TMK until a depth of color suitable for spectrographic measurements is obtained. In each reaction the metal is maintained in excess of the TMK to prevent any interference from the yellow color of unreacted indicator. The light transmittance of these solutions may be measured throughout the visible spectrum, preferably by a Beckman spectrophotometer. The values obtained are plotted as shown in the figure. Observed visually, the aqueous solutions of the metallic compounds appear as follows:

Mercury-Blue-green, strong red dichroism Silver-Rose-magenta Copper-Orange-pink Gold--Blue-purple, red dichroism PalladiumB1uish magenta These colors, indicated by the curves in the figure, are those of :the aqueous solutions only. The same compounds in alcohol, acetone, or chloroform appear much redder in hue. However, the same absorption bands appear in the spectroscope although they are much narrower and more sharply defined.

The analytical methods of the present invention that involve TMK are of added interest when applied to mercury, because of its novel use in the analysisof cyanides. As previously described herein, the novel blue-green compound formed with mercury is completely destroyed by cyanides; in the reaction mercuric cyanide is formed and the original TMK is regenerated. This reaction affords the use of TMK as an internalindicator,

in a volumetric analysis method for mercury or cyanides. For example, solutions of both mercuric nitrate and potassium cyanide are prepared in 0.1, 0.01, and 0.001 molar concentrations. Before carrying out the titrations the solutions are buffered with sodium acetate and a few drops of a 0.1% solution of TMK in acetone are added. When mercury solutions are titrated with cyanide, the color change at the end point is very sharp with 0.1 and 0.01 molar solutions and sufficiently sharp with 0.001 molar solutions. When cyanide solutions are titrated with mercury, the color change is from pale orange to blue; the change shows the same degree of sharpness as the reverse titration.

Another example of this novel method for determining trace amounts of cyanides is as follows:

' 1. To a solution of sodium cyanide and water,

2. Add sodium acetate as a buffer;

3. Add 2-3 drops of a 0.1% solution of TMK in acetone;

4. Add a measured amount of a standard mercuric nitrate solution;

5. Stir the sodium cyanide solution and TMK mixture while adding the mercuric nitrate solution;

6. Stop adding mercuric nitrate when blue color, indicative of an excess of mercury, appears.

In all cases the results are reproducible and the end point is reversible. When accurately standardized solutions are used, it is found that the combining ratio of Hg to CN is exactly 112 in either direction. The presence of chlorides did not interfere with the reaction.

The herein described high color intensity and sharp absorption bands displayed by solutions of TMK in the presence of certain metals provides a novel indicator for colorimetric analysis of these metals. In this type of quantitative analysis, excess reagent must be used to insure complete conversion of all the metal to its colored complex. With TMK as the reagent any excess is preferably destroyed, or removed, to prevent interference by the yellow color-due to the reagent itself. In the herein described reaction with mercury it was found that excess reagent could be removed by extraction with ether, leaving the blue-green mercury compound unaffected in the water layer.

Accordingly, the following novel colorimetric procedure is provided by the present invention: 10 ml. of a solution containing mercury ions is placed in a 30 ml. separatory funnel, together with 0.2 ml. of a solution made up of one part of glacial acetic acid and two parts of a 10% sodium acetate solution; the TMK (0.1% in alcohol) is added drop by drop until the blue green color first formed becomes changed'to a distinct reddish color, indicating a small excess of the TMK. After 10 seconds 6 ml. of ethyl ether is added and the mixture shaken thorough ably With a K1ett colorimeter fitted with a No. 56 filter having a transmission range of 540-590 millimicrons, which corresponds to the most marked absorption band of the mercury compound'as indicated by: the Hg curve in the figure.

The hereindescribed novel method will accurately determine micro traces of the various metals referred to herein. For example: determinations made of solutions containing 0.01, 0.05, 0.1, 0.3, 0.5, 1.0, .1.5, and 2:5 parts per million have been accurately determined. The determinations just quoted give a straight line curve when plotted on a coordinate chart that shows mercury concentrations in parts per million and colorimetric readings in scale units. This readily affords intermediate readings on micro amounts of mercury determined by this method.

Prior to the present invention there "have been no satisfactory reagents for determining' either macro or micro quantities of mercury by a simple procedure. zone) and p-dimethylaminobenzalrhodanine, previously recommended for mercury determinations, have no quantitative significance except as limited colorimetric indicators and then only by following involved and uneconomical procedures. TMK, in the present invention, can be used not only as a colorimetric indicator but as an internal indicator in the volumetric analysis of mercury. This permits the general application of TMK to all analytical methods in which mercury can be used as a reagent.

The present invention also accomplishes the analysis of other herein described metals. The herein described silver complex, for example, is quantitatively destroyed by chlorides when the reaction is carried out in a solvent, such as alcohol, in which the solubility of silver chloride is below the limit of sensitivity of TMK to silver. Under these conditions solutions of chlorides can be titrated directly with standard silver nitrate solutions to a sharp end point, represented by a color change from pale yellow to magenta.

Furthermore, the present invention provides an important advance in the sensitive analysis of carbon monoxide. Prior to the present invention, in the previous palladium method, the gas containing carbon monoxide was passed into an excess of a standardized solution of palladous chloride, the reduced palladium filtered off, and the unused palladium salt measured gravimetrically as the dimethylglyoxime complex.

The present invention provides for the im-' proved analysis of carbon monoxide in the following manner:

1. A measured amount of a mixture of air containing the suspected carbon monoxide is bubbled through a measured amount of a standard solution of palladium chloride and water;

2. A certain amount of the palladium is thereby reduced, if carbon monoxide is present;

3. Filter out and remove this reduced palladium;

4. Add a measured amount of 'I-MK to the thus filtered solution and note the colorimeter reading of the resulting TMK color reaction there- 5. Add an equal, measured amount of TMK to a second, or test amount of the standard palladium chloride solution identical to the first measured, or operation amount of that solution used in Step 1, and note the colorimeter reading of the TMK color reaction in said second solution;

6. The difference between these two colorimeter readings will indicate the amount of carbon monoxide originally present in the mixture of air tested.

By this method minute traces of carbon monoxide, undetectable by prior methods, can be determined.

The absorption curve of the highly colored Dithizone diphenylthiocarba platinumscompound, or platinumcomplex, "closely resembles that .of the silver compound or complex and that of the :paladium compound or complex herein described and therefore :is not shown on the figure. Platinum is readily detectable by "the methods of the presentinvention, in dilutions equivalent to those recited herein for silver.

The structure of the herein described novel metallic derivatives of TMK may be .generally exemplified by the following formula wherein ,Me represents :an equivalent .of any one of the metals in the group comprising mercury, copper, silver, gold, platinum, and palladium, and wherein X represents :an equivalent of a negative radical, such as, for example, a nitrate, a sulphate, or a chloride:

While preferred embodiments of the present invention have been illustrated herein, it is intended that the present invention shall include all embodiments and modifications within the spirit and scope of the appended claims. The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

We claim:

1. The method of determining the concentra tion of metals of a single member of the group consisting of mercury, copper, silver, gold, platinum and palladium which comprises adding p,pbis(dimethylamino) thiobenzophenone to a solution suspected of containing the Single member of the said metals in the form of ions of the group consisting of mercury, cuprous copper, silver, gold, platinum and palladium, identifying the metal by the color of the resultant product, and determining the transmissivity of the solution to light which is a function of the concentration.

2. The method of determining the concentration of mercury which comprises adding 1 ,1 bis(dimethylamino) thiobenzophenone to a solution suspected of containing mercury ions, identifying the metal by the color of the resultant product, and determining the transmissivity of the solution to light which is a function of the concentration.

, 3. A composition of matter consisting of an organic compound of the formula:

Where X is an equivalent of a negative inorganic radical.

4. A method of determining the concentration of mercury solutions and cyanide solutions wherein the concentration of one of the solutions is known which comprises adding p,p'-bis(dimethylamino) thiobenzophenone to a known amount of the mercury solution, thereby coloring the solution, titrating the solution with the cyanide solution until the said color disappears.

5. In the method of qualitatively determining the presence of chemical elements in a. medium by producing a color change in said medium, the

step which comprises adding p,p bis-(dimethylamino) thiobenzophenone to a solution containing a single ionic member of the group consisting of mercury, cuprous copper, silver, gold, platinum and palladium in a suificient quantity to aflirm the presence of one of said members and identifying the metal by the resultant color of the solution.

6. The method of detecting the presence of a metal according to claim 5 wherein the solution is suspected of containing mercury ions.

BERNARD GEHAUF. JEROME GOLDENSON.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Number OTHER REFERENCES Baither, Ber deutsch. Chem. Ges., vol. 20, 1887, pages 1731 to 1734 and 3290-91. 10 Fehrman, Ber deutsch. Chem. Ges., vol. 20,

1887, pages 2857-58.

Arndt et al., Ber deutsch. Chem. Ges., vol. 57, 1924, page 1906.

Laird et al.Determination of Mercury with 15 5-Diphenylearbazide, Ind. and Eng. Chemistry,

vol. No.10, October 15, 1938, page 576. 

3. A COMPOSITION OF MATTER CONSISTING OF AN ORGANIC COMPOUND OF THE FORMULA:
 5. IN THE METHOD OF QUALITATIVELY DETERMINING THE PRESENCE OF CHEMICAL ELEMENTS IN A MEDIUM BY PRODUCING A COLOR CHANGE IN SAID MEDIUM, THE STEP WHICH COMPRISES ADDING P,P''-BIS-(DIMETHYLAMINO) THIOBENZOPHENONE TO A SOLUTION CONTAINING A SINGLE IONIC MEMBER OF THE GROUP CONSISTING OF MERCURY, CUPROUS COPPER, SILVER, GOLD, PLATINUM AND PALLADIUM IN A SUFFICIENT QUANTITY TO AFFIRM THE PRESENCE OF ONE OF SAID MEMBERS AND IDENTIFYING THE METAL BY THE RESULTANT COLOR OF THE SOLUTION. 